The Thai prime minister says anti-government groups could resort to violence before the anniversary of the country's 2006 coup. But the rights groups question whether the threat is sufficient for the government to keep the capital under emergency rule.

The discovery of three unexploded bombs around Bangkok this week prompted Prime Minister Abhisit Vejjajiva to warn of more violence in the coming days, possibly caused by supporters of former Prime Minister Thaksin Shinawatra.

Mr. Thaksin was ousted in a military coup on September 19, 2006. His supporters, known as red shirts, led massive protests earlier this year that choked central Bangkok before the army broke up the demonstrations.

Kiat Sittheeamorn is president of the Thailand Trade Representative Office and a senior member of Mr. Abhisit's Democrat Party. He says the risk of violence is serious.

"We have some concerns over the next couple of weeks that there might be certain movements," Kiat said. "And that's the reason why we have to continue to keep the state of emergency for Bangkok and for a few other provinces in order to ensure that the officers can exercise their duty effectively."

Bangkok has been under emergency rule since April, during the protests. Before they ended, about 90 people - red shirts, bystanders, journalists and soldiers - died in fighting.

Security forces have arrested scores of red shirts and some of their leaders fled the country. Many red shirts now say the movement is in disarray and severely weakened.

Even so, last week, the government stepped up security in Bangkok, placing armed troops at 460 locations, such as railway stations and major government buildings.

Sunai Pasuk is the representative for Human Rights Watch here. While he says the threat appears genuine, he questions the need to maintain the state of emergency. The emergency powers allow the government to ban public gatherings, control the media and detain suspects for 30 days without charge.

"But what Human Rights Watch is deeply concerned is that the government seem to be manipulating fears ? to justify the on-going enforcement of the emergency decree," said Sunai. "All these threats they are real but not to the extent that they will undermine the survival of the Thai state."

Thailand has been gripped by political uncertainties since 2005, when Mr. Thaksin's opponents organized protests against him, which eventually led to the coup.

His critics, mostly from Thailand's urban middle and upper class, say Mr. Thaksin abused his power and was corrupt. His supporters, from rural areas and city slums, say he addressed their needs with programs such as cheaper health care and village development loans.

Mr. Thaksin faces a two-year jail term for corruption charges and lives overseas. But he stays in contact with his supporters, including leaders of the opposition Puea Thai Party.